Various types of inkjet heads are being proposed and developed, one of which is a sharing mode type inkjet head (Patent Documents 1 to 3).
Specifically, the sharing mode type inkjet head ejects ink drops from nozzles connected to a plurality of pressure-generating chambers for generating a pressure by deforming walls composed of an electromechanical conversion means by operating the electromechanical conversion means that are compartmented by the walls.
In recent years, there have been increasing needs for quickly forming an image on various types of media using an inkjet head. For instance, when an image is formed on a non-absorbable recording material or a slightly absorbable recording material, an ink can fail to readily spread on a recording material. Specifically, it is hard to form an image of a solid portion, thereby generating a void or a white stripe. Therefore, there have been reported some needs for slightly widening the ink dot diameter after ink droplets land or slightly increasing the amount of droplets in order to improve image quality.
In response to these needs, Patent Document 1 discloses a method for increasing the volume of droplets by making the pulse width of an expanded pulse (normally 1AL) odd-number times thereof such as 3AL or more.
In addition, Patent Documents 2 and 3 propose increasing the pulse width of an expanded pulse to 1AL or more, aimed at achieving favorable ink ejection and stable high frequency driving.